81131520 has 192 divisors, whose sum is σ = 275184000. Its totient is φ = 20348928.

The previous prime is 81131509. The next prime is 81131551. The reversal of 81131520 is 2513118.

It is a tau number, because it is divible by the number of its divisors (192).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 583611 + ... + 583749.

It is an arithmetic number, because the mean of its divisors is an integer number (1433250).

Almost surely, 2^81131520 is an apocalyptic number.

81131520 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81131520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (137592000).

81131520 is an abundant number, since it is smaller than the sum of its proper divisors (194052480).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81131520 is a wasteful number, since it uses less digits than its factorization.

81131520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 188 (or 168 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 21.

The square root of 81131520 is about 9007.3037031067. The cubic root of 81131520 is about 432.9089230578.

Adding to 81131520 its reverse (2513118), we get a palindrome (83644638).

The spelling of 81131520 in words is "eighty-one million, one hundred thirty-one thousand, five hundred twenty".